Add coverage key to gitlab CI to make badge work

.gitlab-ci.yml

@@ -34,6 +34,7 @@ run_precommit:
   <<: *prepare-env
   script:
     - cd tests/ && ./run_all_cov.sh
+  coverage: '/(?i)total.*? (100(?:\.0+)?\%|[1-9]?\d(?:\.\d+)?\%)$/'
   artifacts:
     when: always
     reports: